A huge search-and-rescue operation continued today for a crew member missing after a tug capsized and sank on the River Thames in London.

A huge search-and-rescue operation continued today for a crew member missing after a tug capsized and sank on the River Thames in London.

Two other crew members were safely rescued after the tug, called Chieftain and which was towing a barge with a crane on it, went down off Greenwich Pier in south London just before 11am.

A section of the river was closed as the search for the missing crew member went on.

The search was being co-ordinated by the Woolwich-based London coastguard and involved police, the Port of London Authority, the fire brigade and lifeboat crews.

A Port of London Authority spokesman said: "It is believed there were three crew members on the Chieftain. Two were safely recovered and were taken ashore. A major search-and-rescue operation is going on."

Thames safety measures were tightened in the aftermath of the 1989 Marchioness riverboat sinking disaster in which 51 people died when their boat was in a collision with a dredger on the Thames near Southwark, south London.

The improved measures included the setting up of the London coastguard which is located at the Thames Barrier Navigation Centre at Woolwich.

Today's sinking follows the death on the Thames last week of Ben Woollacott, 19, a crewman on the Woolwich Ferry.

He fell from the ferry and under its propeller while mooring ropes were being untied.

Paramedics treated the crewman when he was pulled from the Thames, but he was pronounced dead at the scene.

He was the son of Stephen Woollacott, owner of a Thames riverboat company.

Transport for London said today the Woolwich Ferry will be suspended on Monday as staff will be paying their respects at Mr Woollacott's funeral.

Thames River Services and Crown River Cruises are also suspending services on Monday.

A police helicopter is currently above the stretch of river off Thames Street where the boat sank.< A lifeboat deployed when the boat sank is nearby and several ambulances are on stand-by.

The tug and barge are completely submerged.

A second tug boat, which river workers said was also attached to the barge, is still afloat and activity could be seen on deck.

One onlooker said they rushed to the riverside shortly after the incident at 11am but by then the boat was underwater.

One passer-by who witnessed the sinking said: "The front tug seemed to hit a buoy and capsized. It was submerged within a matter of minutes.

"I saw two men being pulled out of the water on the other side of the river.

"All the boats in the area scrambled and were searching for the third man.

"As the minutes dragged on, I started to fear the worst. It was terrible watching and not being able to help."